If you take a slice of meat like beef or ham or pork, you can see the fat and you can cut it off. If something is chopped up and scrunched back together again, like corned beef or luncheon meat or spam, then you can't cut it off. And as these are normally cheaper than "real" meat, they are usually going to be high in fat and have other fillers to bulk them out.
If meat is cheap, there is usually a reason!